In a continuously variable transmission in which a continuously variable transmission mechanism (variator) and a sub-transmission mechanism are combined (hereinafter, referred to as a “CVT with a sub-transmission mechanism”), a shifting region can be enlarged as compared with a normal continuously variable transmission and fuel economy can be improved.
In the case of shifting the sub-transmission mechanism in this CVT with the sub-transmission mechanism, it is possible to suppress a change of a through speed ratio, which is a speed ratio of the entire transmission, before and after a shift and suppress a shift shock by performing a coordinated shift of changing a speed ratio of the variator in a direction opposite to a shifting direction of the sub-transmission mechanism.
JP2012-57710A discloses a CVT with a sub-transmission mechanism having a manual mode of controlling a through speed ratio to a speed ratio corresponding to a gear position selected by a driver. In the manual mode, shift responsiveness is improved by a variator shift of changing the through speed ratio by changing only a speed ratio of the variator according to a shifting operation of the driver.
Further, depending on a shifting region, a gear position of the sub-transmission mechanism is switched by a coordinated shift immediately after the variator shift in preparation for the next shift instruction. This is for the following reason.
For example, if the gear position of the sub-transmission mechanism is a gear position on a high side and the driver instructs to downshift from an M3 speed to an M2 speed of the manual mode, a through speed ratio corresponding to the M2 speed cannot be realized even if the variator is shifted to a lowest side.
Accordingly, when the driver instructs to downshift from an M4 speed to the M3 speed, the speed ratio of the variator is changed to a high side while the gear position of the sub-transmission mechanism is switched to a gear position on a low side by subsequently performing the coordinated shift after the through speed ratio corresponding to the M3 speed is realized by the variator shift.
Since this enables a through speed ratio corresponding to the M2 speed to be immediately realized only by the variator shift when a downshift instruction from the M3 speed to the M2 speed is given, shift responsiveness can be improved.